Nausea and vomiting are significant problems during pregnancy, affecting about 70 to 80% of women during early pregnancy, and about 20% of women throughout pregnancy. In a smaller number of women, about 0.3 to 2%, the symptoms are severe enough to cause significant dehydration, disturbed electrolyte balance, weight loss, and ketosis, which can lead to a condition known as hyperemesis gravidarum. In certain cases, hospital admission may be necessary.
Medications for emesis are available, but none are universally effective. Moreover, medications carry a risk of fetal malformations and their use is discouraged (see C. Broussard et al., “Treating gastro-esophageal reflux disease during pregnancy and lactation: What are the safest therapy options?” Drug Saf. 1998, 19: 325-37). Although fluids and electrolytes can be replenished, and general nutrition promoted in a pregnant woman, nausea and vomiting still cause considerable discomfort, and no ideal treatment is available. It is well known that the gastrointestinal tract is innervated by the vagus nerve, and it has been shown conceptually that stimulation of vagal fibers can suppress experimental vomiting. See Zabara et al., “Neuroinhibition in the regulation of emesis,” Space Life Sci., 1972, 3: 282-92; Zabara, “Neuroinhibition of xylazine induced emesis,” Pharamacol. Toxicol. 1988, 63: 70-74.
Patients often suffer from nausea and vomiting as a result of chemotherapy treatments. For example, chemotherapy treatments for diseases such as cancer, severe forms of connective tissue diseases or inflammatory diseases of the body, or inflammatory or autoimmune disorders of the peripheral or central nervous system can require use of agents that produce nausea, vomiting, or both. Examples of connective tissue diseases or inflammatory diseases of the body include disorders such as lupus erythematosus, rheumatoid arthritis, scleroderma, dermatomyositis, and ulcerative colitis. Examples of inflammatory or autoimmune disorders of the peripheral nerves or central nervous system include disorders such as chronic inflammatory demyelinating polyneuropathy, multiple sclerosis, neurosarcoidosis, central nervous system lupus, central nervous system vasculitis, and monoclonal gammopathy. Finally, some patients experience severe motion sickness. Moreover, the disorders listed above can themselves cause nausea or vomiting. Although medications are available for treating these conditions, none are universally effective.
U.S. Pat. No. 4,981,146 to Bertolucci discloses a nausea control device for electrically stimulating the wrist in the region of the median nerve, at the P6 acupuncture point. However, this treatment for nausea is not universally or completely effective.
Direct vagus nerve stimulation has been used clinically for the treatment of intractable seizures of partial onset (see, e.g., U.S. Pat. Nos. 5,025,807; 4,867,164; and 4,702,254, all to Zabara). According to these Zabara patents, a neurocybernetic prosthesis is placed surgically within the neck, in direct proximity to the vagus nerve. Direct stimulation of the vagus nerve primarily causes localized effects in the area of stimulation. Common symptoms include hoarseness, throat pain, coughing, and dyspnea, paresthesias, and muscle pain, occurring at the time of stimulation. Importantly, there is no evidence to suggest that vagus nerve stimulation causes effects elsewhere in the body or causes birth defects (see E. Ben-Menachem et al., “Gestational outcomes in patients with epilepsy receiving vagus nerve stimulation,” Epilepsia 1998, 39 (suppl 6): 180).
Vagus nerve stimulation has been envisioned as a treatment for disorders other than epilepsy, including psychiatric disorders. Stimulation of other cranial nerves has been envisioned for treating a variety of neurological disorders including voluntary and involuntary disorders; migraine; epileptic seizures; motor disorders; Parkinson's disease; cerebral palsy; spasticity; chronic nervous illnesses and involuntary movement disorders; pancreatic endocrine disorders including diabetes and hypoglycemia; dementia including cortical, subcortical, multi-infarct, Alzheimer's disease and Pick's disease; sleep disorders including central sleep apnea, insomnia and hypersomnia; eating disorders including anorexia nervosa, bulimia and compulsive overeating; and neuropsychiatric disorders including schizophrenia, depression and borderline personality disorder (see U.S. Pat. No. 5,299,569 to Wernicke et al. and U.S. Pat. No. 5,540,734 to Zabara).
Vagus nerve stimulation also has been envisioned for treating heart disorders (see U.S. Pat. No. 5,700,282 to Zabara), hypertension (see U.S. Pat. No. 5,707,400 to Terry, Jr. et al.), endocrine disorders such as diabetes and hypoglycemia (see U.S. Pat. No. 5,231,988 to Wernicke et al.). It also has been envisioned to treat gastric motility disorders such as duodenal ulcers, irritable colon, diverticulosis, and dumping syndrome (see U.S. Pat. No. 5,540,730 to Terry, Jr. et al.). However, the '730 patent does not describe a method or system for treating nausea or vomiting by stimulating the vagus nerve on a patient's neck, and further does not describe stimulator electronics with a power supply arranged outside the patient's body. In the '730 patent, the stimulus generator is implanted in the patient's body, such as below the skin covering the abdomen. An implanted battery supply or other power supply is undesirable for many patients, such as pregnant women, where the source of nausea or vomiting may be transitory.
It would be desirable to provide improved methods and systems for treating nausea and vomiting. It would also be desirable to locate a current source for such methods and systems outside the body, for patients who do not need or desire an implanted power supply or battery operated device. Such methods and systems should overcome the deficiencies of the presently available methods and systems.